Method for modular laser diode assembly

ABSTRACT

A method for laser diode bar assembly. A method for assembling a modular stacked diode array is disclosed, whereby a diode bar is bonded between a pair of conductive spacers, as by soldering, to create a diode submodule. Each submodule, prior to being affixed to a substrate, may be individually pre-tested. Any number of diode bar submodules then may be affixed to a substrate to construct a diode bar array. A stacked array embodiment assembled according to the method provides for efficient cooling of the diode bars and electrical connection between diode bars while maximizing alignment of the diode bars. The spacers are connected to a conductive surface on a heat spreader. In the stacked array, one or more diode bars are alternated in series with two or more conductive spacers, with a series circuit provided from diode bar to diode bar. The spacers hold the diodes spaced apart from insulating grooves in the conductive layer on the substrate. Alternatively, thermally conductive separator fins extend from the heat spreader substrate to contact the diode bars situated between the spacers to promote rapid heat transfer from the diodes while maintaining the diode bars electrically isolated from tie conductive layer on the substrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of application Ser. No.09/170,491, filed Oct. 13, 1998 now U.S. Pat. No. 6,295,307, entitled“Laser Diode Assembly,” which claims the benefit of the filing of U.S.Provisional Patent Application Ser. No. 60/062,106, entitled “LaserDiode Assembly” filed on Oct. 14, 1997. The specifications of both theseprior applications are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention (Technical Field)

The present invention relates to laser diodes, particularly to a laserdiode assembly which promotes accurate spacing and alignment of diodebars, cooling of diode bars and electrical conductivity through thediode bars, as well as modularized assembly and pre-testing.

2. Background Art

Laser diode arrays are in general use in a wide variety of industrialand research applications. Pluralities of diode bars are mounted up on asubstrate to provide the multiplied power of numerous bars, versus theeffect offered by a single bar. To optimize the efficiency of a multiplediode bar array, it is desirable not only that the diode bars beproperly aligned so that their emitter surfaces face the same direction,but electrical conductivity between bars and cooling of the bars shouldbe optimized.

Most efforts in the art have focused upon modes and means of mountingnumerous diode bars quickly and inexpensively. The mounting of numerousbars into a single array historically has been a somewhat labor and/orcost intensive proposition, thus partially impeding the development ofeconomical products and devices incorporating laser diode arrays.

U.S. Pat. Nos. 5,040,187 and 5,284,790, both to Karpinski, show a“monolithic” laser diode array. The disclosure teaches a substratehaving a number of grooves therein, and into which the diode bars areinserted. The substrate ostensibly is flexed into an arc to widen thegrooves; the diode bars are inserted into the temporarily widenedgrooves, after which the substrate is relaxed and allowed elastically toreturn to its normal shape, which results in an effective narrowing ofthe grooves thereby to help hold the inserted diodes in place. A varietyof “submounts” for the array also are taught. However, the methods andconfigurations of the disclosures are not conducive to diode baralignment, as the bars tend to tip and roll within the grooves duringassembly.

U.S. Pat. No. 5,128,951 to Karpinski also shows a particular type oflaser diode array and method of fabrication. The disclosure has to dowith providing an inexpensive mode of manufacturing a diode bar array. Asubstrate is provided with two layers, an upper conductive layerimmediately above and in flush contact with a lower non-conductivelayer. The grooves for receiving the diode bars are cut into thesubstrate so as to completely pierce the upper layer and penetrate intothe lower non-conductive layer. The disclosure purports thereby toprovide a means for mounting diode bars which promotes conductivitybetween bars while also providing heat transfer into the lowerelectrically insulating layer. The diode bars do not have optimalcontact with the “heat sink” lower layer, and maximized alignment of thebars in the grooves also is not taught.

U.S. Pat. No. 5,305,344 to Patel discloses a laser diode array. Thedisclosure teaches diversity in diode bar packing, and a configurationwhich possibly eases the replacement of defective individual bars, butis comparatively complex and expensive.

U.S. Pat. No. 5,311,535 to Karpinski shows a laser diode array whichprovides for laser emission from the minor surfaces of the diode bars.The device involves the disposition of diode bars into a groovedsubstrate. Diode bar alignment is not carefully optimized.

Other United States patents of interest in the field include U.S. Pat.No. 5,644,586 to Kawano et al.; U.S. Pat. No. 5,627,850 to Irwin et al.;U.S. Pat. No. 5,568,498 to Nilsson; U.S. Pat. No. 5,497,391 to Paoli;U.S. Pat. No. 5,418,799 to Tada; U.S. Pat. No. 5,440,577 to Tucker; U.S.Pat. No. 5,394,426 to Joslin; U.S. Pat. No. 5,212,707 to Heidel et al.;U.S. Pat. No. 5,105,430 to Mundinger et al.; U.S. Pat. No. 5,031,187 toOrenstein et al.; U.S. Pat. No. 5,061,974 to Onodera et al; U.S. Pat.No. 5,060,237 to Peterson; U.S. Pat. No. 4,980,893 to Thornton et al.;U.S. Pat. No. 4,947,401 to Hinata et al.; U.S. Pat. No. 4,903,274 toTaneya et al.; U.S. Pat. No. 4,881,237 to Donnelly; and U.S. Pat. No.4,092,614 to Sakuma et al. Nevertheless, a need remains for a means andmethod of providing a laser diode array which at once is simple andeconomical, and yet optimizes proper diode bar alignment to promoteemission efficiency without sacrificing efficient electricalconductivity between, and cooling of, the diode bars. Further, there isa need, addressed by the present invention, for a modular method oflaser diode assembly that permits submodules of an assembly to beindividually tested and/or replaced. Against this background, thepresent invention was developed.

SUMMARY OF THE INVENTION (DISCLOSURE OF THE INVENTION)

The invention includes a wedged array embodiment of a diode barassembly, a stacked array embodiment, and methods and apparatus forassembling the stacked and wedged arrays.

More specifically, the invention includes a method for assembling adiode bar assembly. An aspect of the method is the construction of aplurality of diode submodules, each submodule assembled by the steps of:(a) locating a first conductive spacer upon a planar working surface;(b) disposing a first solder preform, having a melting temperature, uponthe first conductive spacer; (c) placing a diode bar upon the firstsolder preform; (d) disposing a second solder preform having a meltingtemperature upon the diode bar; (e) placing a second conductive spacerupon the second solder preform; (f) compressing the spacers, preformsand diode bar parallel together; (g) heating the solder preforms abovetheir melting temperatures; and (h) allowing the melted solder preformsto harden by cooling, thereby bonding the spacers to the diode bar, andwherein the spacers bonded to the diode bar define a diode submodule.The step of compressing may comprise disposing a weight upon the secondspacer. The step of heating preferably comprises placing the submodulein a controlled heat source while compressing the spacers, solderpreforms, and diode bar.

The inventive method further comprises the assembly of a plurality ofsubmodules into a diode bar array, comprising the step of affixing aplurality of diode submodules, prepared according to steps (a)-(h)above, upon a substrate, the substrate being provided with a pluralityof conductive strips, wherein after affixing the conductive strips arein electrical contact with respective solder preforms; and wherein theplurality of submodules affixed to the substrate define a diode bararray. The plurality of conductive strips preferably comprise solderhaving a melting temperature less than the melting temperatures of thesolder preforms, wherein the step of affixing comprises the steps of:(a) heating the plurality of submodules, the conductive strips, and thesubstrate to a temperature between the melting temperature of theconductive strips and the lowest melting temperature of the solderpreforms; and (b) allowing the melted conductive strips to harden bycooling, thereby bonding the submodules to the substrate. Alternatively,where the plurality of conductive strips comprise solder pre-applied tothe substrate, the step of affixing may comprise the step of applyingepoxy glue between the submodules and the substrate.

Thus there is disclosed a method for assembling a diode bar array, whichcomprises overall steps of: (a) locating a first conductive spacer upona planar working surface; (b) disposing a first solder preform, having amelting temperature, upon the first conductive spacer; (c) placing adiode bar upon the first solder preform; (d) disposing a second solderpreform having a melting temperature upon the diode bar; (e) placing asecond conductive spacer upon the second solder preform; (f) compressingthe spacers, preforms and diode bar parallel together; (g) heating thesolder preforms above their melting temperatures; (h) allowing themelted solder preforms to harden by cooling, thereby bonding the spacersto the diode bar, and wherein the spacers bonded to the diode bar definea diode submodule; and (i) affixing a plurality of diode submodulesprepared according to steps (a)-(h) upon a substrate, the substratebeing provided with a plurality of conductive strips, wherein afteraffixing the conductive strips are in electrical contact with respectivesolder preforms; and wherein the plurality of submodules affixed to thesubstrate define a diode bar array.

A primary object of the present invention is to provide a laser diodeassembly that is economically and simply assembled.

A primary advantage of the present invention is that the laser diodebars in the inventive assembly are optimally aligned to minimize diodeemission wave front distortions.

Another advantage of the invention is the provision of a method forassembling diode bar arrays that permits individual diode submodules tobe individually pre-tested, and separately replaced, as needed.

Other objects, advantages and novel features, and further scope ofapplicability of the present invention will be set forth in part in thedetailed description to follow, taken in conjunction with theaccompanying drawings, and in part will become apparent to those skilledin the art upon examination of the following, or may be learned bypractice of the invention. The objects and advantages of the inventionmay be realized and attained by means of the instrumentalities andcombinations particularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated into and form a partof the specification, illustrate several embodiments of the presentinvention and, together with the description, serve to explain theprinciples of the invention. The drawings are only for the purpose ofillustrating a preferred embodiment of the invention and are not to beconstrued as limiting the invention. In the drawings:

FIG. 1 is an exploded view of one version of the stacked arrayembodiment of the diode bar assembly according to the present invention;

FIG. 2 is a perspective view of the assembly shown in FIG. 1,illustrating the completed assembly;

FIG. 3 is an exploded view of another version of the stacked arrayembodiment of the diode bar assembly according to the invention;

FIG. 4 is a perspective view of the assembly shown in FIG. 3,illustrating the completed assembly;

FIG. 5 is a perspective view from above of a jig apparatus according tothe invention for assembling the assemblies shown in FIGS. 1-4;

FIG. 6A is an exploded view of one version of the wedged arrayembodiment of the diode bar assembly according to the present invention;

FIG. 6B is an end view of the assembly depicted in FIG. 6A, shown fullyassembled;

FIG. 7 is a perspective view, from above, of the assembly shown in FIG.6B;

FIG. 8 is an end view of an assembled alternative version of theembodiment depicted in FIG. 6B;

FIG. 9 is a perspective view, from above, of the assembly depicted inFIG. 8;

FIGS. 10 and 11 are different perspective views of an alternativeembodiment of the assembly shown in FIG. 9, illustrating that theinventive assembly may be provided in curved versions;

FIG. 12 is a perspective exploded view of still another alternativeembodiment of the assembly according to the invention, illustrating anembodiment providing for parallel diode bar circuitry;

FIG. 13 is an exploded end view of the assembly shown in FIG. 12;

FIG. 14 is a perspective view of the embodiment illustrated in FIG. 12,showing the assembly in a fully assembled condition;

FIG. 15 is an end view of the assembly shown in FIG. 14;

FIG. 16 is an exploded perspective view of a diode bar submodule; whichis assembled by one method according to the present invention;

FIG. 17 is a perspective view of the submodule depicted in FIG. 16,shown in an assembled condition; and

FIG. 18 is a side view of a diode bar array, including a plurality ofdiode bar submodules like the submodule of FIG. 17, that is assembledaccording to a method according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS (BEST MODES FOR CARRYING OUTTHE INVENTION)

The present invention relates to laser diode apparatus and methods ofassembly. The apparatus of the invention is an assembly of laser diodebars. By the apparatus and method of the invention, a laser diode barassembly is provided having diode bars that are optimally aligned andmay be densely packed. Parallelism of the diode bars is enhanced anddiode bar curvature is eliminated. The apparatus of the inventionmanifests increased efficiencies in cooling and electrical continuity,and finds ready application in any area in which high powersemiconductor laser arrays are used or desired. In one embodiment of themethod of the invention, the array is composed of a plurality ofseparately constructed sub-modules, which permits individual diode barsto be pre-tested for performance or characteristics before installationon a substrate to define an array, or for individual post-installationreplacement as needed.

The apparatus of the invention features two principal embodiments, a“stacked array” embodiment and a “wedged array” embodiment. Eitherembodiment offers the advantages of superior diode bar alignment andcooling and conductivity efficiency and performance. The two embodimentshave many features in common, but may be manufactured using somewhatdiffering processes as described herein. The user of the invention isfree to select the apparatus embodiment that best suits the particularapplication.

The stacked array embodiment includes four main parts; a plurality oflaser diode bars, thermally conductive and electrically conductivespacers, a thermally conductive and electrically non-conductive heatspreader base substrate, and a coolant manifold. The laser diode barsuseable in the invention are available off-the-shelf. The diode bars areprovided with a layer of gold or other conductive material to provideelectrical continuity. The spacers are parts machined to specification,and typically are fashioned from a metallic alloy. The specification ofthe spacers depends upon the spacing required between diode bars; thus aparticular diode bar assembly may have spacers machined to the specificneeds of the given assembly. The spacers preferably are coated withsolder. The heat spreader base substrate is provided with either groovesor fins in order to electrically isolate the diode bars from thesubstrate. As further explained below, the diodes are sandwichedbetween, and connected to, the spacers. The sandwiched configurationpromotes diode bar alignment and parallelism, as well as enhancingelectrical continuity between diode bars. The spacer-diode assembliesare then attached to the heat spreader substrate, and the substrate maythen be attached to the coolant manifold.

Broadly characterized, the invention thus includes stacked and solderedlayers of laser diode bars and conductive spacers to form an electricalpath for the diode bars in a series arrangement. In alternativeembodiments, the diode bars can be connected can be connected inparallel or a combination of series and parallel circuits. The spacersare coated with a thin layer of material such as solder to facilitateassembly.

The electrically non-conductive heat spreader base substrate featuresmetalized grooves or fins to accept the stacked diode bars and spacers.In one version of the stacked array embodiment, a mounting face of theheat spreader substrate may be metalized or coated with a conductivematerial and grooves cut through the conductive layer. The spacers aresoldered or otherwise conductively connected to the conductive layer,while the diodes are situated “above” spaced apart from the grooves. Inanother desirable version, the heat spreader substrate is provided withperpendicularly extending fins having metalized or otherwise conductivesides. The spacers are soldered or otherwise conductively joined to thefins, while the diodes remain electrically isolated from the substrate.

The practice of the invention includes the optional use of a jigassembly apparatus wherewith the diode bars and spacers are compressedtogether to form a parallel diode bar assembly. The coolant manifold,heat spreader, diode bars and spacers are soldered together for goodthermal conduction. An advantage of the invention is that by selectivelyre-heating selected portions of the laser diode assembly, a individualdiode bars can be removed and replaced as needed.

Attention is invited to FIG. 1, showing elements of a version of the“stacked array” embodiment of the invention. The laser diode barassembly 20 includes a coolant manifold 21, a heat spreader basesubstrate 24, one or more spacers 26, 27, 28 and at least one,preferably a plurality, of laser diode bars 30, 30′. The coolantmanifold 21 is typical to the art in general function and construction.Manifold 21 is a thermally conductive block or element which serves todraw off thermal energy away from the diode bars 30, 30′. The manifold21 may feature passages (not shown) therein through which coolant flowsto promote cooling of the assembly, all according to generally knownprinciples. The manifold 21 optionally may be provided with metal orother thermally conductive fins disposed therein to increase heattransfer. Alternatively, the coolant manifold 21 may be a thermalelectric cooler, also constructed according to generally knownprinciples. In either case, the manifold 21 may be a machined part orcan be purchased off-the-shelf from existing vendors.

The spacers 26, 27, 28 preferably are fashioned from copper or otherconductive material. Each spacer preferably also is coated, e.g., with a0.001- to 0.002-inch thick solder, most preferably a 80/20 gold-tinsolder coating. Alternatively, the spacers 26-28 may be plated, forexample with gold, and thin solder pads carefully situated between thespacers and the diode bars 30, 30′ during the construction of the diodebar assembly 20.

The heat spreader base substrate 24 is machined component composed of arigid, thermally conductive, but electrically non-conductive material,beryllium oxide being a preferable example. Base substrate alternativelymay comprise aluminum nitride. The heat spreader substrate 24 functionsin the assembly 20 to remove heat from the diode bars 30, 30′ withoutproviding an electrical path which shorts out the diode bars 30, 30′. Ofcourse, the substrate 24 ideally has a very high thermal conductivity soto rapidly move thermal energy into the manifold 21. The thickness ofthe heat spreader substrate 24 is minimized if, as in the depictedembodiment, it is to be soldered or otherwise joined to a heat sink suchas the coolant manifold 21 or thermal electric cooler. The spreadersubstrate 24 is cut to the length of the diode bars 30, 30′ and spacers,as suggested by FIG. 1, while the thickness of the base substrate 24 isdependent upon the number of diode bars 30, 30′ desired to be mounted inthe assembly 20. Spreader base substrate 24 is fashioned tospecification such that at least one, and preferably two or more,grooves 32, 32′ are defined in one mounting face 33 thereof, as seen inFIG. 1. Grooves 32, 32′ are parallel, and correspond in number with thenumber of diode bars 30, 30′ to be mounted. As best seen in FIG. 1, themounting face 33 of the base substrate 24 is plated or otherwise coatedwith a conductive layer 34, e.g., of metal. The grooves 32, 32′ aremachined or otherwise formed to fully penetrate the conductive layer 34,such that the walls and bottoms of the grooves are thermally, but notelectrically, conductive. When the diode bar assembly 20 is properlyassembled, the diode bars 30, 30′ are disposed parallel and to thegrooves 32, 32′, but are not inserted therein.

One mode of manufacturing the heat spreader base substrate may be, forexample, to provide a nonconductive base 24 of aluminum nitride on whichan upper plate of conducive material 34 is bonded using high temperatureepoxy. Such basic sub-assemblies of non-conductive bases with anattached plate of conductive material are commercially available. Onceso bonded, the diode bar grooves 32, 32′ are cut into the conductiveplate 34 by either an EDM wire or mechanical cut. The grooves 32, 32′are cut completely through the conductive plate 34. The diode bars 30,30′ may then be inserted into the grooves 30, 30′.

Also as seen in FIG. 1, the spacers 26-28 have a width dimension greaterthan the width dimension of the diode bars 30, 30′. The edges on oneside of the spacers and diode bars are aligned to be flush, so that onthe opposite side of the subassembly, the spacers 26, 27, 28 project orextend equidistantly laterally beyond the diode bars 30, 30′, toward thesubstrate 24, as illustrated. The spacers have a thickness correspondinggenerally to the distance between the grooves 32, 32′, so that the diodebars 30, 30′ are suspended apart from, but parallel, to the grooves whenthe apparatus is fully assembled , as seen in FIG. 2.

Continued reference to FIG. 1 shows that the diode bars 30, 30′ andspacers 26, 27, 28 are placed in alternating contact, with each diodebar 30 located between and in contact with two spacers 26, 27. Thus, thediode bars 30, 30′ and spacers 26, 27, 28 are arranged in a contiguousstacked array of spacers alternated with diode bars. When “sandwiched”in such stacks, in mutual contact, the sub-module or subassembly ofdiode bars 30, 30′ and spacers 26, 27, 28 may be pressed together andsecured by the expedient of heating the subassembly to melt the solder(or equivalent conductive adhesive) on the spacer bars to bind thespacers to the metalized coating on the diode bars. Upon the hardeningof the solder cement, the spacer-diode bars subassembly can bemanipulated as a unit for attachment to the heat spreader substrate 24.A mode and apparatus for assembling the diode-spacer bar subassembly isdescribed hereinafter.

The spacers 26-28 and diode bars 30, 30′ having been secured together inthe alternating array, the spacer-diode bar sub-assembly is fastened tothe heat spreader base substrate 24. After the diode bars 30, 30′ arealigned parallel to the grooves 32, 32′, the extended edges of thespacers 26, 27, 28 are contacted with and soldered to the conductivelayer 34 on the face 33. The back side 35 of the base substrate, whichpreferably also is plated or coated with a conductive metal, is thensoldered or otherwise conductively adhered to the manifold 21.

FIG. 2 depicts the stacked array embodiment of the diode bar assembly inthe fully assembled configuration. The electrically and thermallyconductive spacers 26, 27, 28 hold the diode bars in spaced-apartparallel relation to each other, and also serve to provide theelectrical and physical connection between the diode bars and theconductive layer 34 on the heat spreader base substrate 24. The basesubstrate 24 in turn provides the thermal and physical connectionbetween the spacers 26, 27, 28 and the coolant manifold 21. Notably,because the spacers and diode bars were secured together undercompression, the diode bars are maintained in optimized parallelalignment. The spacers 26, 27, 28 also hold the diode bars 30, 30′ aspaced distance apart from the base substrate 24, thereby thermallyisolating the diode bars to keep them comparatively cool. Nevertheless,the diode bars 30, 30′ are in direct electrical series, as current isfree to flow, e.g. into the bottom of the conductive layer 34, throughthe first spacer bar 26 and into the first diode bar 30, thence into thesecond spacer bar 27 and thence into the second diode bar 30′, into thethird spacer 28, and on out the top of the conductive layer 34. As thebase substrate 24 is a comparative insulator, the circuit iselectrically efficient while heat nevertheless is quickly transferredfrom the spacers 26, 27, 28 through the substrate 24 and into themanifold 21. The circuit thus functions while maintaining the relativethermal isolation of the diode bars 30, 30′. A tremendous advantage ofthis configuration, however, is the parallelism of the diode bars 30,30′ which enhances their transmission efficiency.

FIGS. 3 and 4 illustrate another version of the stacked array embodimentof the inventive diode assembly 20. The component parts and arrangementare substantially similar to the version shown in FIGS. 1 and 2, exceptthat the heat spreader base substrate 24 is alternatively configured. Asshown in FIG. 3, the manifold 21 has the same configuration aspreviously described, and the diode bars 30, 30′ and spacers 26, 27, 28are arranged in the staggered alternating configuration with the widerspacers extending laterally beyond the sides of the diode bars facingthe substrate 24.

In this alternative embodiment, the heat spreader substrate 24 isprovided with at least one, preferably a plurality, of separator fins38, 38′. Separator fins 38, 38′ preferably are constituted from the sameelectrically non-conductive material as the substrate 24 itself; mostpreferably, the substrate is machined to define the fins as integralextensions of the substrate. The separator fins 38, 38′ correspond innumber to the number of diode bars 30, 30′ to be mounted. As shown inFIG. 3, the separator fins 38, 38′ are parallel and extend generallyperpendicular from the mounting face 33 of the substrate 24. The widthof the fins 38, 38′, i.e., the distance the fins extend from themounting face 33, is approximately equal to the difference in widthsbetween the diode bars 30, 30′ and the spacers 26, 27, 28. Thus, thefins 38, 38′ can fully occupy the gaps between the extended edges of thespacers 26, 27, 28 when the edges of the spacers are brought intocontact with the mounting face 33 of the substrate 24, as furtherexplained hereafter.

As best illustrated by FIG. 3, the sides of the fins 38, 38′ (i.e. thefin surfaces perpendicular to the face 33) are coated with a thinconductive layer 39, preferably gold, which may be deposited bysputtering or other known coating methods. Notably, the distal, exposedends of the fins 38, 38′ are not coated with a conductive layer, butinstead remain uncovered and thus electrically non-conductive. Theconductive layer 39 also is provided upon the mounting face 33 along astrip thereof immediately adjacent to both sides of each fin 38, asillustrated in FIG. 3. The strip of conductive layer 39 (e.g.sputter-coated gold) on the face 33 corresponds in width generally withthe thickness of a spacer 28, so that the edge of a spacer may contactand substantially cover the conductive layer 39.

FIG. 4 shows this second version of the stacked array embodiment of theassembly 20 in a fully assembled condition. As mentioned, thespacer-diode bar subassembly, comprising the spacers 26, 27, 28alternated with the diode bars 30, 30′ may be prepared first bycompressing the spacers and diode bars in their stacked arrangement andthen heating the subassembly to flow the solder on the spacers tocontact the metalized surfaces of the diode bars. Upon cooling of thesubassembly, it can be handled as a unit and attached to the heatspreader substrate 24.

The assembly 20 is finished by bringing the spacers 26, 27, 28 intocontact with the conductive layer 39 on the mounting face 33 andseparator fins 38, 38′. As seen in FIG. 4, the separator fins 38, 38′are inserted into the space between the spacers 26, 27, 28 until theends of the fins contact the edges of the diode bars 30, 30′. With thespacers 26-28 so positioned, the spacers are in physical and electricalcontact with the conductive layer 39 on the face 33 and the fins 38,38′. The assembly may then be heated to flow the solder on the spacersand/or the conductive layer 39, thereby securing the spacers to the fins38, 38′ and mounting face 33.

When assembled as depicted in FIG. 4, this version of the stacked arrayembodiment of the laser diode assembly 20 functions very similarly tothe version previously described. Notably, the distal ends of theseparator fins 38, 38′ are in physical contact with the laser diode bars30, 30′. This contact offers the significant added advantage of enhancedheat transfer from the diode bars 30, 30′ directly to the heat spreadersubstrate 24, as thermally energy flows directly from the diode barsinto the fins. Thermal energy is then carried from the fins to themanifold 21. Because the distal ends of the fins are not covered withany of the conductive layer 39, there is no electrical contact betweenthe diode bars 30, 30′ and the substrate. The physical contact of thefins 38, 38′ with the diode bars 30, 30′ promotes the structuralintegrity and durability of the overall assembly 20.

The electrical flow is essentially as previously described. A circuitcan be completed through the diode bars 30, 30′ due to the electricalconductivity of the spacers 26-28, the conductive layer 39, and themetalized contacts on the diode bars themselves.

In lieu of conventional soldering methods, the apparatus 60 of theinvention may be integrated using other bonding methods. For example,the diode bars 30, 30′ may be bonded to the conductive layers 34 or 39using an atomic welding process. The atomic welding process relies uponthe exothermic reaction of the monatomic hydrogen (Brown's Gas)combining into diatomic hydrogen to generate the bond between twoadjacent materials. This process may be used for joining two widelydissimilar materials to one another, due to the atomic level energyinteractions that take place during the exothermic reaction. Thus,materials having widely dissimilar physical characteristics, such as theelectrically non-conductive heat spreader base 24 and the electricallyconductive plate 34 may be joined by atomic welding. Similarly, it maybe desirable to bond the diode bars 30, 30′, 30″ directly to a berylliumsubstrate by atomic welding.

Attention is invited to FIG. 5, showing an assembly jig 42 according tothe present invention, which is useable for assembling the stacked arrayembodiments of the diode bar assembly 20. The assembly jig 42 is a meansfor precisely aligning and interconnecting the spacers 26-28 and thediode bars 30, 30′, 30″. The proper alignment is achieved by compressingthe spacers and the diode bars together while situating them againstspecially tilted planar surfaces.

The jig assembly 42, is somewhat larger in size than the diode barassembly 20 to be manufactured. Jig assembly 42 includes a jig table 44,back wall 46, side wall 47, and clamp 48. The jig table 44 defines aworking surface 50 upon which the subassembly of diode bars 30, 30′ isaccomplished. The working surface 50 is machined to be planar with aminimum of warp or wave. Preferably, the working surface is tilted intwo axes. The tilted disposition promotes, by the force of gravity, theproper alignment of the spacers 26-28 and diode bars 30, 30′ in theassembly jig 42. As shown in FIG. 5, the working surface 50 is tiltedtoward the side wall 47 at a small angle x (for example, but not by wayof limitation, between approximately one and ten degrees) with respectto horizontal. The working surface 50 of the jig table 44 preferablyalso is tilted toward the back wall 46 at a small angle y (for example,between approximately one and approximately five degrees) with respectto horizontal. Accordingly, the working surface 50 has an overall pitchor cant toward the inside corner defined by the intersection of theworking surface, the back wall 46, and the side wall 47. Items placedupon the jig table 44 tend, therefore, to slide or roll by the force ofgravity toward both walls 46, 47.

The back and side walls 46, 47 preferably but not necessarily areperpendicular to the tilted working surface 50, alternatively, and forsimplicity of construction, the walls 46, 47 may be vertical. During thepractice of the invention, the walls 46, 47 are fixed in position inrelation to the jig table 44.

Two plates of microscope glass 52, 53 are used in the practice of theinvention to provide for extremely smooth, flat, low-friction surfacesagainst which the diode bar-spacers subassembly may be compiled. Oneglass slide 52 rests upon the working surface 50 with its edges abuttingthe walls 46, 47, while the other 53 stands flush against the side wall47 with its edges against the working surface 50 and the back wall 46.

The assembly jig 42 also includes a clamp 48. Clamp 48 provides a meansfor applying a compressive force acting toward and against the back wall46. As seen in FIG. 5, therefore, the clamp 48 is used to controllablypush the diode bar-spacers subassembly against the back wall 46, therebyto compress together the spacers 26-28 and diode bars 30, 30′. The clamp48 may take any number of forms, and may be, for example, spring-loadedor screw-actuated. A tension spring embodiment may involve the use ofhelical springs to pull a push pad 55 toward an immobile anchor on or inthe back wall 46; alternatively, a threaded screw rod orcompression/tension spring combination may be incorporated to push thepush pad 55 toward the back wall 46 from an anchor fixed in relation tothe immobile jig table 44. Any number of suitable clamping arrangementsare available to one of ordinary skill in the art.

One method of assembling a stacked array embodiment of the diodeassembly 20 apparatus of the invention may now be briefly described. Thediode bars 30, 30′ preferably are kept in a clean room environment andare handled only with a vacuum chuck having a soft silicon tip or othermeans for manipulating without damaging the diode bars. The diode bars30, 30′ preferably are stored in a vacuum or nitrogen environment toprevent oxidation of the diode bar metalization. Oxidized metalizationlayers on the diode bars may interfere with reliable bonding duringsoldering processes.

The diode bars 30, 30′ preferably are cleaned prior to assembly, such asultrasonically with trichloride. If the diode bars are stored in agel-pack, it is preferred to remove them by pulling a vacuum on the backside of the gel-pack to release the diode bars. The diode bars are thenremoved using a vacuum chuck.

The spacers 26, 27, 28 preferably are stored in dry nitrogen. Thespacers are cleaned prior to assembly with a suitable cleanser, such ashydrochloric acid, and then rinsed, first with deionized water and thenwith isopropyl alcohol.

Referring collectively to FIGS. 1-5, the clean microscope glass 52, 53is situated flush against the two walls 46, 47. The spacers 26, 27, 28and diode bars 30, 30′, 30″ are placed in an alternating pattern in theassembly jig 42. While FIG. 5 illustrates the use of four spacers 26,27, 28, 29 and three diode bars 30, 30′, and 30″, it is understood thatany number of diode bars, according to user preference, can be stackedwith a spacer between each diode bar. The diode bars 30, 30′ aredisposed on the working surface 50, with the emitter sides of the diodesfacing down in contact with the glass 52. Thus, the long edges of thediode bars and spacers rest upon the microscope glass 52 on the workingsurface 50 of the jig table 44. The long side of a first spacer 26 isplaced flush against the back wall 46. The short ends of the diode bars30, 30′ contact the other microscope glass 53, and the bars 30, 30′, 30″and spacers 26, 27, 28, 29 are loaded in an alternating pattern, each inflush contact with adjacent components. Due to the tilt of the workingsurface 50 toward the side wall 47, gravity mildly forces the narrowends of the spacers 26-29 and the narrow ends of the diode bars 30, 30′,30″ against the glass 53 on the side wall 47, thereby aligning thosecomponents with respect to the x-axis shown. The tilt of the workingsurface 50 toward the back wall 46 similarly causes the diode bars 30,30′, 30″ and spacers 26-29 to fall flush against one another therebypromoting alignment with respect to the y-axis shown.

The clamp 48 is then actuated to press the stacked array of spacers anddiodes toward the back wall 46, with the result that the spacers anddiode bars are squeezed between the push pad 55 and the back wall 46.This compression effectively promotes parallelism of the diode bars 30,30′, 30″ and fosters excellent bonding between the spacers 26-29 and thediode bars.

With the spacers 26-29 and diode bars 30, 30′, 30″ thus clamped in theassembly jig 42, the electrically non-conductive heat spreader substrate24 is then disposed upon the stacked diode bar-spacers subassembly. Inthe version of the assembly 20 featuring a grooved substrate 24 (FIGS. 1and 2), the grooves 32, 32′ are aligned with the diode bars so that thediode bars do not contact the heat spreader substrate 24. The physicalseparation of the diode bars 30, 30′, 30″ from the substrate 24, due tothe presence of the grooves 32, 32′ and the support provided by thespacers 26, 27, 28, 29 eliminates solder bridging between adjacent diodebars that would lead to electrical shorts between bars. The top edges ofthe spacers 26-29 positively contact the conductive layer 34, however,and the substrate is thus supported upon the spacers, as seen in FIG. 5.In the case of the finned version of the assembly 20, the fins 38 areinserted between the spacers 26-29, and the substrate 24 rests upon thediode bars 30, 30′, 30″ as well as the spacers. As mentioned, however,only the spacers 26-29 are in electrical contact with the conductivelayer 39 (FIG. 3).

A small weight 56 having a flat face then is placed, flat face down, ontop of the heat spreader substrate 24 as shown in FIG. 5. The weight 56pressing downward upon the clamped spacers and diode bars improves thebonding of the assembly 20. It will be evident to one of ordinary skillin the art that alternative modes of pressing downward, besides the useof a weight, may be employed. Any suitable equivalent means ofcontrollably compressing the sub-assembly against the working face 50 ofthe jig will also suffice, such as the use of a spring-loaded orscrew-driven clamp.

The assembly jig 42, together with the diode bar assembly 20, is thenplaced into a vacuum heat chamber, for example at about 280° C. (to meltan 80/20 gold-tin solder) for approximately ten minutes. The temperatureand time may be varied depending upon the solder type. The clamp 48holds the components in parallel alignment during heating. The heat ofthe chamber melts and flows the solder between the spacers 26-29 and theconductive layer 34 or 39 on the substrate 24, and between the spacersand the diode bars 30, 30′, 30″. Upon removal from the chamber andcooling, therefore, the solder bonds together the components of theassembly 20, with the diode bars 30, 30′, 30″ electricallyinterconnected via the spacers 26-29. The clamp 48 may then be released.Electrical leads (not shown) can then be soldered or otherwiseelectrically connected to the end spacers 26, 29 of the stacked assembly20 using a solder having a melting point lower than the solder used tobind the assembly itself.

Finally, the assembly 20 is electrically connected to a power supply andtested for temperature versus wavelength, and electrical power inputversus optical power output. If any of the individual diode bars 30,30′, or 30″ are determined to fall below specification, the assembly 20may be re-heated to re-melt the solder cement, and the defective diodebar(s) removed and replaced.

The use of stacked array laser diode assemblies according to theinvention permits the process and apparatus to be modularized. Inmodular laser diode assembly, diode bars are individually processed andthen affixed to the substrate. Modularized assembly is beneficial, as itpermits more accurate and particularized placement of the diode bars, aswell as testing and replacement on a specific basis rather than ingross.

Attention is invited to FIGS. 16-18, which illustrate the modularizedlaser diode assembly according to the present invention. According tothis aspect of the invention, a laser diode assembly is constructed of aplurality of sub-modules 200 attached to a common substrate 24, as bestseen in FIG. 18. This aspect of the invention is similar, in many of itsoverall aspects and components, to the stacked array embodiment seen inFIGS. 1-4, and the foregoing discussion of that embodiment will informthe disclosure of the method and apparatus of the modularized diodeassembly and array disclosed hereafter.

FIG. 16 indicates the mode of manufacture of a single submodule 200. Thesub-module is manufactured in a manner similar to that described abovefor stacked arrays generally, i.e., by stacking in generally horizontalstrata. A working surface 50 (optionally tilted as described above) isprovided upon which the submodule 200 is assembled. The assembly issimilar to the construction of a sandwich. A conductive spacer 27 isplaced flush upon the working surface 50. A solder preform 73, comprisedof a strip or square of thin, pre-formed solder cut to correspondgenerally in lateral size to the spacer 27, is placed flush upon thespacer 27. The spacer 27 is sized to correspond generally to the laserdiode bar 30. A second solder pre-form 73′ is then placed upon the topsurface of the laser diode bar 30, and a second spacer 26 is placed uponthe solder preform 73′ to cap off the submodule 200.

The entire submodule 200 arranged as shown in FIG. 16, thus is situatedupon the working surface 50. A weight 56 is then disposed upon thestacked submodule 200 to provide a downward force tending to compresstogether the various components of the submodule 200. The stackedsubmodule 200 (which when properly arranged will appear substantially asindicated in FIG. 17) while disposed between the working surface 50 andthe compressive weight 56, may then be placed in an oven, where thetemperature is elevated to melt the solder preforms 73, 73′ and thusbind the spacers 26, 27 to the diode bar 30. The weight 56 is selectedto provide the desired compressive force to squeeze the submodule 200together during the melting of the solder preforms 73, 73′. After thesolder preforms 73, 73′ have melted, the submodule 200 is cooled topermit the solder to harden and thereby bond the main elements 26, 30,27 of the submodule together.

Advantageously the submodule 200, thus assembled and as appearing inFIG. 17, can then be separately tested to determine or confirm itsindividual optical characteristics. Submodules not passing predeterminedperformance standards may then be rejected or re-manufactured prior toincorporation into a full laser diode bar array 208, such as that shownin profile in FIG. 18. According to the invention, therefore, nosubstandard submodule 200 need be incorporated into an array 208, assubmodules 200 may be pre-tested, either individually, or by usingstatistical sampling methodologies, at the time of submodule manufacturebut prior to the completion of an array.

A laser diode array 208 according to the invention including a pluralityof substantially identical submodules 200 is depicted in FIG. 18. Aplurality of submodules 200 is disposed upon a pre-tinned thermalsubstrate 24 to accomplish the assembly of a diode array 208. Substrate24 is provided with pre-applied strips of solder 202, 202′ each pair ofsolder strips 202, 202′ separated by a uniform gap 205. The solderstrips 202, 202′ are fashioned from a solder having a melting pointsubstantially lower than the melting point of the solder pre-forms 73,73′ used to bond the submodule 200 together as described above. Eachsubmodule 200 is placed upon the pre-tinned substrate 24 so that thediode bars 30 are positioned above, and aligned with, a correspondinggap 205 in the substrate solder 202, 202′. The solder strips 202, 202′do however, contact the solder layers 73, 73′ of each submodule 200,permitting electrical flow through the diode bar 30.

As indicated in FIG. 18, a plurality of submodules 200 are thus arrangedin physical parallel relation upon the pre-tinned substrate 24, andthere held in position, as by robotic clamping or the like. Thesubmodules 200 do not touch each other, but rather are separated by aseries of parallel separation gaps 210. With the plurality of parallelsubmodules 200 held in place against the substrate 24 so that theconductive preforms 73, 73′ are in electrical contact with the solderstrips 202, 202′, but the diode bars 30 are not, the entire array 208may be heated to a temperature in excess of the melting point of thesolder strips 202, 202′ but below the melting point of the solderpreforms 73, 73′. The melting of the solder strips 202, 202′ occurs tobond the several submodules to the substrate 24 in the appropriatearrangement seen in FIG. 18. Upon the cooling of the array 208 to hardenthe solder strips 202, 202′, the submodular laser diode array 208 isready for further testing or incorporation as a component of largerdevices. Advantageously, each submodule 200 in an array 208 may beindividually removed and replaced as needed by simply heating andre-heating the corresponding portion of the substrate 24 to melt theselected strips 202, 202′ adjacent the submodule to be replaced.

Thus, the present invention includes the foregoing method for assemblinga diode bar assembly. An aspect of the method is the construction of aplurality of diode submodules 200, each submodule 200 assembled bylocating the first conductive spacer 27 upon a planar working surface50, disposing the first solder preform 73, having a melting temperature,upon the first conductive spacer 27, placing the diode bar 30 upon thefirst solder preform 73, disposing the second solder preform 73′ havinga melting temperature upon the diode bar 30, placing the secondconductive spacer 26 upon the second solder preform 73, compressing thespacers 26, 27, preforms 73, 73′ and diode bar 30 parallel together,heating the solder preforms 73, 73′ above their melting temperatures,and then allowing the melted solder preforms to harden by cooling,thereby bonding the spacers 26, 27 to the diode bar 30. The spacers 26,27 bonded to the diode bar 30 define a diode submodule 200. The step ofcompressing may involve disposing a selected weight 26 upon the secondspacer 26, although alternative known methods of compressing thesubmodule 200 are within the scope of the invention. The step of heatingpreferably includes placing the submodule 200 in a controlled heatsource while compressing the spacers 26, 27, solder preforms 73, 73′ anddiode bar 30.

The inventive method extends to the assembly of a plurality ofsubmodules 200 into a diode bar array 208, by the step of affixing aplurality of diode submodules, prepared as described above, upon thesubstrate 24, the substrate being provided with a plurality ofconductive strips 202, 202′. After the affixing step, the conductivestrips are in electrical contact with respective solder preforms 73,73′, and the plurality of submodules affixed to the substrate 24 definethe diode bar array 208. The plurality of conductive strips 202, 202′preferably are made from solder having a melting temperature less thanthe melting temperatures of the solder preforms 73, 73′. The step ofaffixing includes the steps of heating the array 208 to a temperaturebetween the melting temperature of the conductive strips 202, 202′ andthe lowest melting temperature of the solder preforms 73, 73′,(consequently melting the conductive strips but not the solderpreforms), and then allowing the conductive strips to harden by cooling,thereby bonding the submodules 200 to the substrate 24. Alternatively,where the plurality of conductive strips 202, 202′ are strips of solderpre-applied to the substrate 24, the step of affixing may include thestep of applying epoxy glue between the submodules and the substrate.

The overall method for assembling a diode bar array, thus includes inits ambit the steps of: (a) locating the first conductive spacer uponthe planar working surface; (b) disposing the first solder preform,having a melting temperature, upon the first conductive spacer; (c)placing the diode bar upon the first solder preform; (d) disposing thesecond solder preform upon the diode bar; (e) placing the secondconductive spacer upon the second solder preform; (f) compressing thespacers, preforms and diode bar parallel together, preferably by placinga weight upon the stacked components; (g) heating the solder preformsabove their melting points; (h) allowing the melted solder preforms toharden by cooling to bond the spacers to the diode bar to fashion adiode submodule; and (i) affixing a plurality of diode submodules upon asubstrate, the substrate being provided with a plurality of conductivestrips, wherein after affixing the conductive strips are in electricalcontact with respective solder preforms. The situation of the pluralityof submodules against the substrate may be accomplished using roboticdevices known to the manufacturing art, to permit rapid and preciselocation prior to affixation.

An alternative embodiment of the invention is the laser diode assemblyapparatus 60 depicted in FIGS. 6A, 6B and 7. This assembly 60 is a“wedged array” assembly, wherein individual wedges are used (instead ofexternal compression, such as from a jig) to force the diode bars intoproper parallel alignment. The wedged array embodiment has fourprincipal types of components: A base substrate, conductor strips,wedges, diode bars, and tension wires.

In this embodiment, a series of small wedges are inserted into a taperedgroove and pulled down into position against am associated series ofdiode bars. Applicants have successfully manufactured the wedges andcoated them with a desirable thickness of indium.

The base substrate 74 is fashioned from substantially the same material,for example beryllium oxide, and serves most of the same functions asexplained herein for the heat spreader base substrate 24 included in thestacked array embodiment (FIG. 1) of the invention. The base substrate74 of the wedged array is machined or otherwise formed to specifiedshapes as explained herein. The conductive strips 67, 68, 69, 70, 71, 72may be made from a variety of materials and assume a variety ofdifferent shapes. The shapes and numbers of conductive strips 67-72illustrated in FIGS. 6A and 6B are disclosed as a useful example, butnot by way of limitation. The conductive strips 67-72 serve as a meansfor providing electrical contact and connection between adjacent diodebars, for example between diode bar 62 and bar 63, or between bar 63 andbar 64 shown in the drawings. The conductive strips 67-72 in oneembodiment are thin strips of bendable, electrically conductive metalalloy, for example indium solder, which are separately fashioned forinsertion into the grooves 76, 77, 78 as shown in FIGS. 6A and 6B.Alternatively, the conductive strips 67-72 may be deposited on the keysurfaces of the substrate 74 by a vapor or sputter coating or depositionof indium solder or other conductive metal.

The wedges 62, 63, 64 are comprised of copper or other electricallyconductive material. The wedges 62, 63, 64 serve a primarily structuralfunction, and therefor need to be substantially rigid andnon-compressible. However, they also are electrical contacts, and musteither be made from a conductive material or be coated with a conductivelayer by any suitable method.

The diode bars 30-30′″ are of the same type as described for the stackedarray embodiment of the invention, and are commercially available. Eachbar has a principal surface from which the laser energy is emitted. Thiswedged array embodiment of the invention 60 allows a plurality of barsto be reliably aligned in parallel arrays to enhance array performance,particularly to minimize wave front distortions. The tension wires 80,81, 82 are used to force the wedges 62-64 into corresponding grooves76-78 in the substrate 74 and maintain their position during heating ofthe assembly 60.

FIG. 6A is an exploded end view of a single assembly 60, depicting how,in one embodiment, the various components are positioned to complete theassembly shown in end view in FIG. 6B and in perspective view in FIG. 7.In the illustrated example, the assembly includes three conductivewedges 62, 63, 64, four laser diode bars 30, 30′, 30″ and 30′″, and sixconductive strips 67, 68, 69, 70, 71, 72 which are mounted upon aspecially configured base substrate 74. It is understood, however, thatvarious versions of the assembly 60 according to the invention can havevarious numbers of these components according to the intended use anddesired specification of the apparatus. As best illustrated in FIG. 6A,the wedges 62-64, diode bars 30-30′″ and conductive strips 67-62 aredisposed into shaped grooves 76, 77, 78 in the base substrate 74. Asshall be further explained, wires 80, 81, 83 corresponding in number tothe number of diode bars are used to hold the assembly 60 togetherduring manufacture.

The base substrate 74 features a major surface 84 having at least one,preferably a plurality of grooves 76, 77, 78 therein. The grooves aresubstantially identical in configuration, except that outside groves(e.g. groove 78) may have one side wall defined by an adjacent secondsubstrate (not shown) or some other support member. Description of onegroove 76, and the components 62, 68, 30′, and 69 that are insertablydisposed therein serve to describe like grooves and components situatedparallel in the substrate 74 as shown. Each groove, for example groove76, is defined by a first wall 88 and a second wall 89, these walls 88,89 being nonparallel and converging toward a bottom 90 of the groove, asbest seen in FIG. 6A.

Combined reference to FIGS. 6A and 6B shows that a diode bar 30′ isdisposed vertically into the groove 76 with its emitter surface upwardso as to be proximate to the major surface 84 and therefor free to emitenergy away from the major surface 84 of the substrate. A conductivewedge 62 is placed in electrical contact with the diode bar 30′ andforcibly inserted into the groove 76 between the diode bar 30′ and thesecond wall 89, thereby pressing the diode bar against the first wall88. This pressing action fosters optimum alignment of the diode bar 30′and, when repeated for the diode bars (e.g. 30″, 30′″) in each of therespective other grooves (77, 78) promotes parallelism between diodebars for maximum efficiency of the assembly 60. As mentioned, theinventive apparatus may feature a single groove with a diode bar andwedge therein, or, preferably, a plurality of diode bars disposed withincorresponding ones of a plurality of grooves, with each groove definedby a first wall and a second wall, the walls being nonparallel andconverging toward a bottom of each groove. As seen in FIGS. 6A, 6B and6B, each first wall 88 preferably is perpendicular to the major surface84 of the substrate 74. Also preferably, the second wall 89 is inclinedin relation to the major surface 84 and intersects the bottom 90 of thegroove at an angle α.

The wedge 62 preferably has a first face 91 and a second face 92intersecting at an angle substantially equal to the geometric complementof angle α, (i.e. 90°−α). Accordingly, when a wedge 62 is pressedbetween the second wall 89 and a diode bar 30′ previously disposed intothe groove 76, the first face 91 slides in flush contact along thesecond wall 89 of the groove 76, and the wedge pushes the diode 30′firmly and flush against the first wall 88 of the groove. The result isan optimally aligned diode bar 30′. As best seen in FIG. 6B, a smallchannel optionally may be centrally provided in the butt of each wedge62 to receive and hold a tension wire 80.

The process for assembling a wedged array assembly 60 is explained. Inone embodiment, the conductive strip 69 on the first wall 88 of thegroove 76 is previously deposited or sputter-coated upon the first wall88; alternatively and in many instances preferably, the conductivestrips, for example, strips 67, 68, 69 pertaining to the groove 76 areseparately shaped, as shown in FIGS. 6A and 6B, from thin conductivebands of malleable alloy. The base substrate 74 first is positioned andtemporarily secured onto any suitable rigid mounting surface or fixture.The strips 67, 69 and 7i are laid in against the first walls 88 of thegrooves. The diode bars 30, 30′, 30″, 30′″ are then disposed into therespective grooves until the diode bars bottom in the grooves, with thebars resting against the first-laid strips 67, 69, 71. While theconductive character of the wedges and the metalized coating on thediode bars may obviate the need, it may be desirable next to place thesecond set of conductive strips 68, 70, and 72 against the diode bars topromote complete bonding of the assembly 60 and electrical contactbetween the wedges and the diode bars. With the conductive strips 68, 70and 72 resting upright against the diode bars, the wedges 62, 63, 64 areplaced in position into the space between the second-laid strips 68, 70and 72 and the second faces 88 of the several grooves (e.g. 76, 77, 78).The process of inserting a strip 69, then a diode 30′, then a strip 68and then a wedge 62 is repeated until all the grooves are populated,although it is understood that with the proper equipment the process maybe accomplished for two or more grooves simultaneously.

With the grooves populated with diode bars, conductive strips, andconductive wedges, the tensioning wires 80, 81, 82 are situated upon thebutts at the tops of the wedges as shown in FIG. 6B. The tensioningwires 80, 81, 82 may be laid into small channels cut into the butts ofthe wedges, if desired, to provide a means for maintaining the wires inproper aligned position for forcing the wedges. With the wires in placeupon respective ones of the wedges 62, 63, 64, tension is applied to thewires to push the wedges downward into the grooves 76-78. A sufficienttension is applied by any appropriate external means to drive the wedgesdownward, with the first face 91 of each wedge 62 riding down the secondwall 89 of each groove 76; in many instances, any given wedge 62 willmove downward under the force applied by the tensioning wire 80 untilthe tip of the wedge bottoms against the bottom 90 of the groove 76.However, this is not necessarily the case, as the object is to securelypress the diode bar 30′ firmly against the first wall 88, and thetension applied to the wire 80 is that sufficient to accomplish thispurpose. During this step of the process, a suitable temporary externalvertical support (not shown) may be supplied to hold the outside diodes30, 30′″ to hold them in place against lateral shifting.

FIG. 7 shows how the completed assembly 60 may appear when completed andprepared for soldered bonding. The entire assembly 60 then is placedinto an appropriate oven or other controlled heat source. While thetension is maintained upon the wires 80, 81, 82 to maintain the wedgesand diode bars in alignment, the heat source is activated to melt theconductive strips 67-72 and inter-bond the entire assembly 60. Uponcooling to harden the solder cement, the tensioning wires may beremoved.

Other shapes of strips 67, 68, 69 are possible without departing fromthe scope of this invention. For example, the strips 67 and 69 may beformed from a single integral strip bent into the shape of an “N”, withan additional section (not shown) extending from the top of strip 67 tothe bottom of strip 69 and which lays along the second wall 89 of thegroove 76. Such an N-shaped integral strip then could be laid into thegroove 76, with the section strip 67 against the first wall of the firstgroove, the intermediate strip section along the second wall 89 of thesecond groove 76, and the section strip 69 laid in against the firstwall 88. The diode bar 30′ is then placed, another strip (i.e. 68) islaid in separately against the bar 30, and the wedge inserted betweenthe intermediate section of the N-shaped strip and the second strip 68.

Due to the small size of the wedges 62, 63, 64 and diode bars 30-30′″,and the requirement that small conductive strips 68, 70, 72 preferablyare installed between the diode bars and the first walls (e.g. 88) ofthe grooves in the substrate 74, the final assembly optionally may befacilitated by manipulating the wedges and diode bars as a single unit.In lieu of an assembly process including insertion of a diode barfollowed by insertion of a wedge, the wedge 62 and diode bar 69 may beassembled as a unit. The secondary conductive strip 69 is bonded on theside of the diode bar opposite the wedge 62 during the process ofbonding the wedge and diode bar together. This allows the assemblyprocess to consist of simply disposing the wedge/diode bar/conductivestrip sub-assemblies into the provided groove (e.g. 76).

It is observed, therefore, that the conductive strip 69 functions as ameans for providing serial electrical contact between diode bar 30′ inthe groove 76 and diode bar 30′ in the adjacent groove 77, since thestrip 69 extends between the diode bar 30′ and the conductive wedge 63,which is in electrical contact with the diode bar 30″ in groove 77. Theseries connections between the diode bars 30′, 30″ is completed by theoptional use of another conductive strip disposed between the wedge 63and the inclined second wall of groove 77, and a third conductive strip70 between the wedge and the second diode bar 30″. But, as mentioned,all three conductive strips optionally can be integrated into aplurality of single conductive strips insertable into the adjacentgrooves 76, 77.

In a further alternative embodiment, the wedged array assembly isassembled using the atomic welding process. If the atomic weldingprocess is employed, no conductive coating or strips 67, 69, 71 areprovided for bonding the diode bars to the substrate base 74 (e.g.aluminum nitride). Instead, the wedges 62-64 are fashioned from anelectrically non-conductive material, and atomic welding utilized tobond the wedge/diode subassemblies to the substrate 74. Similarly, diodebars may be soldered into place into a nonconductive base of aluminumnitride using the atomic welding process with a conductive solder.Conductive strips are not required in this approach in order to bond thesolder to the non-conductive base.

FIG. 7 shows the assembly 60 as it might appear prior to being placed inan oven chamber for soldering. The tensioning wires 80, 81, 82 are thenremovable subsequent to cooling.

Removal of the tensioning wires after the assembly 60 has been completedmay be facilitated by providing for the insertion of very small tangsinto the tops of the wedges 62-64 during their fabrication. A smallcutoff block may be incorporated into the initial wire deformation moldfor manufacture of the wedges, which allows the small tang to beintegrated into the wedge. This permits easier handling of the wedgeassemblies, with the wire being broken off at the tang after the diodeassembly 60 is completed.

FIGS. 8 and 9 illustrate that the use of tensioning wires is whollyoptional. Any other suitable means, such as planar clamps forsimultaneously compressing down on all the wedges 62, 63, 64, discreteweights disposed upon corresponding ones of the wedges, a single largeweight, or the like, may also be employed; the principal factor involvedin selecting a means for forcing the wedges downward it that all thewedges be pressed into their respective grooves 76-78 at the same time,and with approximately equal force, in the direction indicated by thedirectional arrows of FIG. 8. FIG. 9 discloses the general appearance ofan assembly 60 where tensioning wires are not employed to force thewedges into position. Instead, a clamp (not shown) for example can beused to compress the tops of the wedges 62, 63, 64 toward the bottom ofthe substrate 74 to maintain the assembly 60 during bulk soldering. Forthis purpose the wedges 62, 63, 64 may be provided with broad, planartops as seen in FIGS. 8 and 9.

An advantageous feature of the invention, particularly of the embodimentshown in FIGS. 8 and 9, is that curvilinear assembles can be produced.In all the embodiments, the grooves 76-78 are disposed in adjacent rows.Straight, rectilinear, parallel rows (FIGS. 6A-9) are, of course, moreeasily machined or otherwise formed into the substrate 74, andrectilinear wedges and diode bars are more readily produced oravailable. In an alternative version illustrated in FIGS. 10 and 11, therows of grooves 76, 77, 78 are parallel, but are curved. Curved wedges62, 63, 64 and curved diode bars 30, 30′, 30″, have generally equalradii of curvature substantially corresponding to the curvature of thegrooves 76, 77, 78 formed in the substrate 74. Using a clamping orweighting mode of pressing the wedges 62-64 into the grooves in thesubstrate 74 the curved diode bars 30-30′″ are pressed into place withinthe grooves in a uniform, parallel curvilinear array.

FIGS. 12-15 illustrate another version of the stacked array embodimentof the invention which allows for parallel lead powering of individualdiodes. This version is similar to the configurations of FIGS. 6A-9, inthat it utilizes wedges to orient and secure the diode bars mutuallyparallel and perpendicular to the base, e.g. a beryllium oxidesubstrate. However, instead of connecting the diodes bars in series, thediode bars are connected in parallel by means of a wedge frame andmultiple conductor bar.

FIGS. 12 and 13 show the individual components, which include a basesubstrate 94, a wedge frame 96, a plurality of diode bars 30, 30′, 30″,30′″, and a conductor bar 98. The respective functions of these elementsis substantially the same as the like elements previously described,except for the added provision of the conductor bar 98 (made forexample, from copper) to provide for parallel circuitry.

FIGS. 12 and 13 illustrate that the conductor bar 98 comprises aplurality (corresponding to the number of diode bars desired to bemounted in the assembly) of longitudinally disposed, mutually parallel,generally fin-like conductive members 111, 112, 113 extendingapproximately perpendicularly from a planar base or bridge member 114.Electrical current may flow from one conductive member 111, to the nextadjacent member 112 by means of the bridge member 114. The overallelectrical conductivity of the conductor bar 98 provides the parallelelectrical contact between one diode bar 30 in one groove 76 and asecond diode bar 30′ in an adjacent second groove 77 (FIG. 13).

Reference is made to FIGS. 12 and 13. The base substrate 94 is similarin material, form and function to the substrates of previous describedembodiments, except that the substrate does not have a solid bottom.Instead, the upstanding, tapered, chocks 100, 101, 102 areinterconnected only by end trusses 103, 104 fixed across the ends of thechocks. Thus, the chocks 100, 101, 102 are held together in spaced-apartrelation by the end trusses 103, 104, thereby defining narrowlongitudinal slits or apertures 106, 107 between respective adjacentchocks (FIG. 13). The apertures 106, 107 are sized and disposed toreceive there through corresponding ones of the conductive members 112,113, so that the conductive members 111, 112, 113 maybe placed incontact with the parallel vertical faces of the chocks 100, 101, 102when the substrate 94 is lowered down onto the conductor bar 98.

The diode bars 30, 30′, 30″, 30′″ are substantially similar to the diodebars previously described for other embodiments of the invention. Thediode bars 30, 30′ 30″, 30′″ are provided on their longer vertical faceswith a conductive coating, strip, or solder, for example conductivesolder 117 on the inside face of diode bar 30 in FIG. 13.

The wedge frame 96 is best shown in FIGS. 12 and 13. The wedge frame 96is best characterized as including a plurality of wedge sections 118,119, 120 extending between two end frame members 121, 122. The wedgesections 118, 119, 120 correspond generally in form and function withthe wedges 62, 63, and 64 of previously described versions of the wedgedarray embodiment, except that the wedge sections optionally may becomparatively much longer axially than an individual wedge 62. Wedgesections have inclined surfaces 123,124 generally functioning the sameas the inclined first face 91 on the individual wedges 62 of otherversions (FIG. 6A). The end frame members 121, 122 hold the wedgesections 118, 119, 120 together but in spaced-apart parallel relation,so that there are longitudinal slits 127, 128 into which the diodes 30′,30″ and chocks 101,102 can be firmly inserted, as indicated by FIG. 15.

The assembly of the wedged, parallel connected array 60 is evident fromthe foregoing, but one mode thereof nevertheless is briefly explainedhere. The base substrate 94 is securely but removably positioned in asuitable mounting tool or fixture (not shown). The conductor bar 98 isinserted upward through the base substrate 94, with the conductivemembers 112, 113 disposed through the apertures 106, 107 in thesubstrate; the protruding conductive strips 111, 112, 113 areimmediately adjacent to corresponding faces of the chocks 100,101, 102running the length of the substrate 94. A strip of solder is formed intoa suitable shape and laid in between each diode bar 30-30′″ and theconductive members 111,112, 113, and the diodes inserted into thegrooves between the conductive members and the chocks 100-102. Anothersolder or other conductive strip can be provided on the other, exposedside of each diode bar, if required. The conductive wedge frame 96 isthen placed upon the diode bars 30-30′″ with the wedge sections 118-120aligned between the diode bars and the inclined faces of the chocks100-102. The wedge frame 96 is then pressed downward with sufficientuniform pressure to slide the wedge sections down along the inclinedsurfaces of the chocks, thereby forcing the diodes firmly against theconductive members 112, 113. As a result of this uniform, wedge-drivenaction, the diodes are optimally aligned, both as mutually parallel, aswell as perpendicular to the end trusses 103, 104 and the conductivebridge 114 generally defining the bottom of the assembly 60.

By this means, the invention provides parallel electrical contactbetween a diode bar 30′ in a first groove 76 and a second diode bar 30″in an adjacent second groove 77, where the substrate 94 defines theplurality of apertures 106, 107 there through, and the parallel contactmeans includes the conductor bar 98, which has at least one firstconductive member 112 insertable through the aperture 106 in thesubstrate for electrical contact with the wedge section 118 in the firstgroove 76; the second conductive member 113 is insertable throughanother aperture 107 in the substrate for electrical contact with thesecond diode 30″ in the second groove 77. The conductive bridge member114 connects the two conductive members 112, 113 to complete a parallelcircuit.

FIGS. 14 and 15 show the assembly 60 with the wedge sections 118-120fully inserted to press the diode bars 30-30′″ into proper position. Theassembly 60 may then be placed into the controlled heat source to meltthe solder and bond the entire assembly, as previously explained.

In the forgoing disclosure, the wedges 62-64 and wedge sections 118-120are described as being inserted downward in the vertical direction. Itis evident to one of skill in the art that the wedges can bemanufactured to allow for horizontal insertion instead. Also, allconductive strips alternatively may be provided by masking off theappropriate portions of the substrate 24 or 94, and electricallyconductive material sputtered or otherwise coated on the selectedappropriate key surfaces.

Although the invention has been described in detail with particularreference to these preferred embodiments, other embodiments can achievethe same results. Variations and modifications of the present inventionwill be obvious to those skilled in the art and it is intended to coverin the appended claims all such modifications and equivalents. Theentire disclosures of all references, applications, patents, andpublications cited above, and of the corresponding provisionalapplication, are hereby incorporated by reference.

What is claimed is:
 1. A method for assembling a diode bar assembly,comprising tie steps of: (a) locating a first conductive spacer upon aplanar working surface; (b) disposing a first solder preform, having amelting temperature, upon the first conductive spacer; (c) placing adiode bar upon the first solder preform; (d) disposing a second solderpreform having a melting temperature upon the diode bar; (e) placing asecond conductive spacer upon the second solder preform; (f) compressingthe spacers, preforms and diode bar parallel together; (g) heating thesolder preforms above their melting temperatures; and (h) allowing themelted solder preforms to harden by cooling, thereby bonding the spacersto the diode bar, and wherein the spacers bonded to the diode bar definea diode submodule.
 2. The method of claim 1 wherein the step ofcompressing comprises disposing a weight upon the second spacer.
 3. Themethod of claim 1 wherein the step of heating comprises placing thediode submodule in a controlled heat source while compressing thespacers, solder preforms, and diode bar.
 4. The method of claim 1further comprising the steps of; preparing a plurality of diodesubmodules according to steps (a)-(h) in claim 1; and affixing theplurality of diode submodules upon a substrate, the substrate beingprovided with a plurality of conductive strips, wherein after the stepof affixing the plurality of diode submodules upon the substrate, theconductive strips are in electrical contact with respective solderpreforms; and wherein the plurality of diode submodules affixed to thesubstrate define a diode bar array.
 5. The method of claim 4 wherein theplurality of conductive strips comprise solder having a meltingtemperature less than the melting temperatures of the solder preforms,and wherein the step of affixing the plurality of diode submodulescomprises the steps of: (a) heating the plurality of diode submodules,the conductive strips, and the substrate to a temperature between themelting temperature of the conductive strips and the lowest meltingtemperature of the solder preforms; (b) allowing the melted conductivestrips to harden by cooling, thereby bonding the diode submodules to thesubstrate.
 6. The method of claim 4 wherein the plurality of conductivestrips comprise solder pre-applied to the substrate, and wherein thestep of affixing the plurality of diode submodules further comprises thestep of applying epoxy glue between the diode submodules and thesubstrate.
 7. A method for assembling a diode bar ray, comprising thesteps of: (a) locating a first conductive spacer upon a planar workingsurface; (b) disposing a first solder preform, having a meltingtemperature, upon the first conductive spacer; (c) placing a diode barupon the first solder preform; (d) disposing a second solder preformhaving a melting temperature upon the diode bar; (e) placing a secondconductive spacer upon the second solder preform; (f) compressing thespacers, preforms and diode bar parallel together; (g) heating thesolder preforms above their melting temperatures; (h) allowing themelted solder preforms to harden by cooling, thereby bonding the spacersto the diode bar, and wherein the spacers bonded to the diode bar definea diode submodule; (i) repeating steps (a)-(e) to prepare a plurality ofdiode submodules; and (j) affixing the plurality of diode submodulesupon a substrate, the substrate being provided with a plurality ofconductive strips, wherein after the step of affixing the plurality ofdiode submodules, the conductive strips are in electrical contact withrespective solder preforms; and wherein the plurality of diodesubmodules affixed to the substrate define a diode bar array.
 8. Themethod of claim 7 wherein the step of compressing comprises disposing aweight upon the second spacer.
 9. The method of claim 8 wherein the stepof heating comprises placing the diode submodule in a controlled heatsource while compressing the spacers, solder preforms, and diode bar.10. The method of claim 9 wherein the plurality of conductive stripscomprise solder having a melting temperature less than the meltingtemperatures of the solder preforms, and wherein the step of affixingcomprises the steps of: (a) heating the plurality of diode submodules,the conductive strips, and the substrate to a temperature between themelting temperature of the conductive strips and the lowest meltingtemperature of the solder preforms; (b) allowing the nelted conductivestrips to harden by cooling, thereby bonding the diode submodules to thesubstrate.
 11. The method of claim 9 wherein the plurality of conductivestrips comprise solder pre-applied to the substrate, and wherein thestep of affixing further comprises the step of applying epoxy gluebetween the diode submodules and the substrate.